This invention relates to microencapsulated particles. In a more specific aspect, this invention relates to microencapsulated particles that are useful in electroluminescent applications. This invention also relates to a process for the microencapsulation of these particles.
This invention will be described in detail with specific reference to the microencapsulation of phosphor particles. However, this invention will be understood as applicable to the microencapsulation of other substance particles, such as pharmaceuticals, organic solvents, organic oils, pigments, dyes, epoxy resins, inorganic salts, etc.
In addition, this invention is applicable to the microencapsulation of polymer (or polymeric) light-emitting diodes (also referred to as PLEDs) and to the microencapsulation of organic light-emitting diodes (also referred to as OLEDs).
In general terms, PLEDs are thin film displays that are created by sandwiching an undoped conjugated polymer between two proper electrodes at a short distance. The polymer emits light when exposed to electricity. PLEDs enable fill spectrum color displays.
In general terms, OLEDs are display devices that sandwich carbon-based films between two charged electrodes, one a metallic cathode and one a transparent anode, usually being glass. The organic films consist of a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport layer. When voltage is applied to the OLED cell, the injected positive and negative charges recombine in the emissive layer and create electoluminescent light.
Microencapsulated particles are known in the prior art. Bayless et al. U.S. Pat. No. 3,674,704 (1972) discloses a process for manufacturing minute capsules, en masse, in a liquid manufacturing vehicle wherein the capsules contain water or aqueous solutions. This patent discloses a specific process for manufacturing minute capsules wherein the capsule wall material is poly(ethylene-vinyl acetate) that is hydrolyzed to a narrowly specified degree (38-50 percent hydrolyzed).
Bayless U.S. Pat. No. 4,107,071 (1978) discloses microcapsules having a capsule core material surrounded by a relatively impermeable, densified protective wall and also discloses a process of manufacturing such microcapsules.
General encapsulating processes which utilize a liquid-liquid phase separation to provide a capsule wall material which envelops the capsule core material to be encapsulated are disclosed in Miller et al. U.S. Pat. No. 3,155,590; Powell et at. U.S. Pat. No. 3,415,758; and Wagner et al. U.S. Pat. No. 3,748,277.
Other prior art references disclose the encapsulation of electroluminescent phosphors; for example, see Budd U.S. Pat. No. 5,968,698 (1999). Additionally, the prior art discloses the coating of luminescent powders with a coating which comprises silicon dioxide; see Opitz et al. U.S. Pat. No. 5,744,233(1998).
Phosphor particles are used in a variety of applications, such as flat panel displays and decorations, cathode ray tubes, fluorescent lighting fixtures, etc. Luminescence or light emission by phosphor particles may be stimulated by applications of heat (thermoluminescence), light (photoluminescence), high energy radiation (e.g., x-rays or e-beams) or electric fields (electroluminescence).
For various reasons, the prior art fails to provide microencapsulated particles having the desired properties of impermeability to moisture and extended release capabilities. Thus, there is a need in the industry for microencapsulated particles having significantly improved properties.
Briefly described, the present invention provides microencapsulated particles which have an increased resistance to the adverse effects of moisture and which are able to function over an extended period of time (i.e., extended release capabilities). The present invention also provides a process for the microencapsulation of these particles.
The above-described advantages of the microencapsulated particles of this invention are evident when compared to similar microencapsulated particles manufactured according to the prior art (that is, not manufactured according to the present invention).
As used in this application, the following terms have the indicated definitions:
xe2x80x9cImpermeability to moisturexe2x80x9dxe2x80x94the ability to prevent or substantially eliminate the intake of moisture and thereby avoid the adverse effects of moisture.
xe2x80x9cImprovedxe2x80x9dxe2x80x94as compared to microencapsulated particles that are disclosed in the prior art and are not microencapsulated according to the present invention.
As will be seen in greater detail below, the microencapsulated particles of this invention have other characteristics that are either equivalent to, or significantly improved over, the corresponding characteristics of the prior art microencapsulated particles.
Accordingly, an object of this invention is to provide microencapsulated particles.
Another object of this invention is to provide microencapsulated particles having improved impermeability to moisture.
Another object of this invention is to provide microencapsulated particles having extended release capabilities.
Another object of this invention is to provide microencapsulated phosphor particles.
Another object of this invention is to provide microencapsulated polymer light-emitting diodes.
Another object of this invention is to provide microencapsulated organic light-emitting diodes.
Still another object of this invention is to provide microencapsulated phosphor particles having improved impermeability to moisture.
Still another object of this invention is to provide microencapsulated phosphor particles having extended release capabilities.
Still another object of this invention is to provide a process for the microencapsulation of particles.
Still another object of this invention is to provide a process for the microencapsulation of particles to produce microencapsulated particles having improved impermeability to moisture.
Still another object of this invention is to provide a process for the microencapsulation of particles to produce microencapsulated particles having extended release capabilities.
Yet still another object of this invention is to provide a process for the microencapsulation of phosphor particles.
Yet still another object of this invention is to provide a process for the microencapsulation of polymer light-emitting diodes.
Yet still another object of this invention is to provide a process for the microencapsulation of organic light-emitting diodes.
Yet still another object of this invention is to provide a process for the microencapsulation of phosphor particles to produce microencapsulated phosphor particles having improved impermeability to moisture.
Yet still another object of this invention is to provide a process for the microencapsulation of phosphor particles to produce microencapsulated phosphor particles having extended release capabilities.
These and other objects, features and advantages of this invention will become apparent from the following detailed description.